ORDINARY CHONDRITES - MULTIVARIATE STATISTICAL-ANALYSIS OF TRACE-ELEMENT CONTENTS

We used standard multivariate Discriminant Functions, borrowed from Linear Discriminant Analysis and Logistic Regression, to compare contents of mobile trace elements (Co, Au, Sb, Ga, Se, Rb, Cs, Te, Bi, Ag, In, Tl, Zn, Cd) in various populations of L4-6 or H4-6 chondrites. To aid in our analysis we developed a non-standard Randomization-Simulation method that permits probability assignments on a distribution-free basis. Because the sample database for Antarctic L4-6 chondrites is very limited, we could not establish that mildly and strongly shocked (< 22 GPa and greater-than-or-equal-to 22 GPa, respectively) populations differ compositionally. For non-Antarctic L4-6 chondrites, where the sample data-base is larger and the degree of shock-loading in the strongly shocked population is greater on average, a highly significant compositional difference is evident. This difference probably reflects shock-induced loss of mobile trace elements from parent material of the strongly shocked population. We believe that the case for compositional difference between Antarctic and non-Antarctic H4-6 chondrite populations, as well as between these populations of L4-6 chondrites, is now conclusively established. Various lines of evidence demonstrate that for various sorts of meteorites, especially H4-6 chondrites, the Antarctic/non-Antarctic compositional difference is not due to trivial (terrestrial) causes but rather to preterrestrial differences in the genesis of their parent materials.